[Asterisk-Users] unsolicited NOTIFY messages from Asterisk

[Chris A. Icide]

Olle E. Johansson wrote:

>Chris A. Icide wrote:
>  
>
>>Note however, that in the unsolicited NOTIFY that Asterisk sends for
>>MWI, it includes a ;tag= as part of the NOTIFY.  This will break some
>>devices as they will not accept the NOTIFY because the tag doesn't match
>>any transaction that is open.  The correct way to send an unsolicited
>>NOTIFY would be without the tag altogether.
>>    
>>
>
>That's interesting. Any suggestions on such a device? I haven't seen that.
>
>I guess if they do that, it's ok, since sending unsolicited NOTIFY is
>theoretically wrong anyway. If the phone software wants to support it,
>they wouldn't bother with the tag, I guess.
>
>/O
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Olle,

Yes, a Metaswitch softswitch (and I suspect some other softswitches 
would as well).  It returns a 403 error if you send a NOTIFY for MWI to 
it with a tag attached.

This is a little different implementation.  The Metaswitch is providing 
the end user (over PSTN) service, and when a phone goes unanswered, it 
sends a the call to asterisk over sip.  I extract the phone number that 
was originally dialed from the SIP Header using the dialplan command for 
reading sip header messages, and send the call to voicemail.  Now I have 
to send back indication that a message exists.

Since the Metaswitch isn't sending a subscribe for every single line, we 
have a push model.  So we push out MWI, but Asterisk tags the push, and 
the Metaswitch rejects it since it has no previous transaction with a 
matching tag.

I patched the code so it won't send a tag on an MWI Notify for my own 
use, but it's specific to this implementation and would cause problems 
where a subscribe has been sent.

-Chris
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